Automobiles and vehicle traffic are well known aspects of everyday life. Statistics based on traffic patterns, driver demographics, and traffic flow may be valuable to city planners, advertising consultants, billboard companies, or environmental agencies. To meet the demand for such information, different "roadside" systems for counting passing vehicles have been developed. The prior art includes car counting systems that rely upon pressure sensors, acoustic devices, metal detectors, or infrared devices. These and other devices have been used notwithstanding their various drawbacks.
The cost of measurement equipment and the cost of conducting traffic tests may be prohibitively high in many cases. For example, pressure sensitive hoses commonly used to count cars on a short-term basis may cost hundreds of dollars apiece, and they require personnel for installation, maintenance, and removal. In addition, such hoses inherently have a very limited lifespan because they are continually driven over by heavy vehicles. As another example, pressure sensitive plates or inductive sensors may be buried under a road surface to create an effectively permanent measuring device. However, these buried devices can cost thousands of dollars apiece, and the cost of installation (which includes the removal and repaving of a portion of the road) may prohibit their use.
None of the conventional car counting systems are 100% accurate in their measurements. However, many prior art systems are used infrequently and during only a small sample period to gather data that will be relied upon for months or years to come. While such systems may be acceptably accurate during the brief testing period, the actual traffic patterns will inevitably demonstrate long term variations. In addition, if the data gathered during the brief sample period is not representative of ordinary traffic conditions, then any calculations or planning based on the data will be inaccurate. Furthermore, many prior art devices are not designed to constantly and accurately monitor or measure traffic volume for long periods of time. Thus, it is desirable to have a car counting system that has sufficient long-term accuracy, and is capable of operating in a continuous manner.
Some prior art devices may be limited to measuring only one phenomenon, such as a numerical count of the vehicles. In some cases, two similar devices are used in series to gather counting data and speed data. Furthermore, if both traffic directions of a road are to be monitored, then more devices must be utilized. Obviously, when more than one device is used, the cost of gathering data is increased. For this reason, there is a need for a versatile system that can be utilized to measure more than one characteristic of passing vehicles.